Polymerization process

Abstract

Polymerization processes for ethylene and at least one mono-1-olefin comonomer having from about three to eight carbon atoms per molecule in the presence of a twice-aged catalyst system comprising chromium supported on a silica-titania support and a trialkylboron compound is provided. Novel ethylene copolymers also are produced.

That which is claimed is:  
     
       1. A polymerization process comprising contacting under slurry polymerization conditions at a temperature within a range of about 200° F. to about 226° F. (about 93° C. to about 108° C.) in an isobutane diluent: 
       a) ethylene monomer;  
       b) at least 1 mono-1-olefin comonomer having about three to eight carbon atoms per molecule;  
       c) a catalyst system comprising chromium supported on a silica-titania support, wherein said support comprises from about 1 to about 10 weight percent titanium, based on the weight on the support, wherein said catalyst system is aged twice and wherein the first aging is at a substantially neutral pH and wherein the second aging is at an alkaline pH, said catalyst system has a pore volume within a range of about 0.5 to about 1.3 ml/g, a surface area within a range about 150 to 400 m 2 /g, and said catalyst system has been calcined at a temperature within a range of about 800° F. to about 1300° F. (about 427° C. to about 704° C.);  
       d) about 1 to about 6 mg/kg, based on total reactor contents, of a trialkylboron compound; and  
       e) recovering an ethylene/mono-1-olefin copolymer.  
     
     
       2. A process according to claim  1  wherein said comonomer is selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and mixtures thereof. 
     
     
       3. A process according to claim  2  wherein said comonomer is 1-hexene. 
     
     
       4. A process according to claim  1  wherein said reactor temperature is within a range of about 210° F. to 220° F. 
     
     
       5. A process according to claim  1  wherein said titania of the silica-titania support is coprecipitated with the silica. 
     
     
       6. A process according to claim  1  wherein said trialkyboron cocatalyst is present in the reactor in an amount within a range of 2 to about 4 mg/kg. 
     
     
       7. A polymerization process comprising contacting under slurry polymerization conditions at a temperature within a range of about 210° F. to about 220° F. in an isobutane diluent: 
       a) ethylene monomer;  
       b) 1-hexene comonomer;  
       c) a catalyst system comprising chromium supported on a silica-titania support, where in said support comprises from 2 to 8 weight percent titanium, based on the weight on the support, wherein said catalyst system is aged twice and wherein the first aging is at a substantially neutral pH and wherein the second aging is at an alkaline pH, said catalyst system has a pore volume within range of 0.8 to 1.2 ml/g, a surface area within a range of 250 to 350 m 2 /g, and said catalyst system has been calcined at a temperature within a range of 1100° F. to 1200° F.;  
       d) about 2 to about 4 mg/kg, based on total reactor contents, of a triethylboron cocatalyst; and  
       e) recovering an ethylene/1-hexene copolymer.